This invention concerns a process for recovering heat from a heat source A, to provide it to a heat source B, and comprising a heat accumulation step.
The use of fossil fuels such as coal, crude oil or natural gas does not raise problems of heat storage since such fuels can be used without difficulty at the very moment of energy demand. On the contrary, some of the new heat sources require storage capacity for utilization for example in the case of the solar energy which is collected in a discontinuous and time and weather contingent manner.
Thermal energy may be stored by means of a liquid and/or solid material, as sensible heat and/or latent heat of physical phase changes. The use of the sensible heat of a substance to store thermal energy suffers from two major disadvantages: on the one hand, the temperature of the material varies as soon as a heat transfer occurs, resulting in poor efficiency of the system; on the other hand, the amount of heat stored per volume unit is low. Conversely, thermal storage by means of a material involving the use of the latent heat of transformation offers the two following advantages: In the case of a pure substance, the heat transfer is effected at constant temperature during the change in state and more energy is involved. Nevertheless, at a temperature lower than the melting point of the material, the heat transfer in a solid medium cannot be achieved except by conduction, and this is a limitation to the process flexibility.